1. Field of the Invention
The present invention relates to an ink jet recording apparatus having a maintenance unit, i.e. a mechanism that performs a maintenance process on a recording head in the apparatus for maintaining the printing performance of the recording head. The present invention also relates to a head maintenance method, a software program for implementing the head maintenance method, and media on which the program is recorded or carried.
2. Description of the Related Art
Ink jet recording apparatuses such as printers are equipped with an ink supply source in the form of an ink cartridge or the like, a recording head having a plurality of nozzles, and an ink supply passage extending between the ink supply source and the recording head nozzles. Printing is executed by drawing ink from the supply source through the supply passage and ejecting ink droplets from the nozzles onto a recording sheet.
Although this arrangement generally works quite well to produce high quality printed output, certain problems tend to arise after an extended period of printer nonuse. When a substantial period of time elapses during which no ink is ejected from the nozzles, water evaporates from the nozzles thereby increasing the viscosity of the remaining ink, or bubbles enter the recording head through the nozzle. To cope with these problems, an ink suction mechanism is sometimes provided to perform a head maintenance operation which involves drawing ink from the nozzles and discharging it to the outside. By periodically performing such a head maintenance operation, the recording head can be maintained in a state in which it can execute proper printing.
Some ink jet recording apparatuses are also provided with a wiping mechanism to perform a different type of head maintenance operation. The wiping mechanism employs an elastic adsorbing mechanism to wipe away foreign matter such as paper dust, ink and the like which have adhered to the surface on which the nozzles are formed. The foreign matter has access to the nozzle forming surface by way of a small gap between the nozzle forming surface and the recording sheet. When such foreign matter adheres to the nozzle forming surface, the nozzles become clogged or the recording sheet may get stained by the ink build up on the nozzles. By periodically carrying out this type of head maintenance operation, the recording head can be maintained in a state in which it can execute proper printing. Note that the maintenance operation used in this specification may be also referred to as a head recovery operation or head cleaning operation among the skilled persons. Hereinafter an operation such as an ink sucking process executed by the ink suction mechanism and a wiping process executed by a wiping mechanism may be referred to as a cleaning operation.
An ink jet recording apparatus provided with an ink suction means and a wiping means arranged as described above is disclosed in, for example, Japanese Unexamined Patent Publication No. 4-255361. Furthermore, an ink jet recording apparatus for restoring a recording head periodically after a predetermined period of time is disclosed in, for example, Japanese Unexamined Patent Publication No. 2-92548.
Conventionally, the head maintenance processing is carried out each time the predetermined period of time elapses or each time a predetermined amount of printing is completed. In either case, the head maintenance process is carried out during a time when no printing operation is being performed because a print operation cannot be interrupted for the execution of the head maintenance process.
In the situation when the predetermined period of time elapses or when the predetermined amount of printing is completed just before printing is started, the head maintenance processing is carried out prior to the start of print operation. In this case, even though a print command may have been issued, the print operation is not carried out until after the head maintenance process is completed. This has the undesirable effect of increasing the time between the issuance of a print command and the actual execution of the print operation.
Similarly, if the head maintenance processing is triggered at a time during which the printer is executing one of a series of successive print operations, the printer will complete the present printing operation, after which the head maintenance process will be executed. After the head maintenance process is completed, the next printing operation will be started. Thus, there is a period of printing xe2x80x9cdown timexe2x80x9d between the completion of one print operation and the start of another while head maintenance processing is executed. This is also undesirable in that it increases the overall time it takes to complete the series of print operations.
Thus, when head maintenance processing is carried out in the conventional manner, there is some chance that head maintenance may be triggered at an inconvenient time such as between the issuance of a print command and the completion of a print operation or during the execution of a series of print operations which are to be successively carried out at small intervals. When either of these situations occurs, completion of the printing operation or series of printing operations will be undesirably delayed.
Therefore, it is an object of the present invention to overcome the aforementioned problems.
In view of the above-noted problems, another object of the present invention is to provide an ink jet recording apparatus which reliably executes a head maintenance process to maintain the quality of the print operation while minimizing the disruption such maintenance operation may have on the printing process or those using the recording apparatus.
A further object of the invention is to provide a method for performing the head maintenance process of the present invention.
Still another object of the invention is to provide a program of instructions (i.e., software) for implementing the head maintenance process method of the present invention, and media on which the program is recorded or carried.
According to one aspect of the present invention, an ink jet recording apparatus is provided that includes a recording head having at least one nozzle through which ink droplets are ejected, and a maintenance unit for executing or performing a maintenance operation on the recording head under the direction of a head maintenance drive controller. The ink jet recording apparatus comprises at least one counting device, such as a timer and/or counter, that counts at least one physical quantity, such as elapsed time and/or an amount of print since a last maintenance operation was performed, to obtain at least one magnitude (i.e., the elapsed time and/or the amount of print value) indicative of a degree of operativeness of the recording head, and also counts a non-print period of time during which no printing operation is performed by the recording head and compares the non-print period of time with a reference period of time. The degree of operativeness represents the degree of necessity to recover or clean the recording head. In accordance with this aspect of the invention, the controller controls the maintenance unit in response to the counting device(s) such that the maintenance unit performs a new maintenance operation when either of the following conditions is met:
(a) the at least one magnitude exceeds a first value; or
(b) the at least one magnitude exceeds a second value but does not exceed the first value and the non-print period of time is greater than the reference period of time.
According to another aspect of the invention, the ink jet recording apparatus comprises a timer that measures the elapsed time since the last the head maintenance process was performed and compares the elapsed time with a first period of time and a second period of time which is less than the first period of time. When the elapsed-time is greater than the second period of time, the same timer or a different timer measures a non-print period of time during which no printing is performed by the recording head and compares the non-print period of time with a third period of time. The head maintenance drive controller controls the execution of the head maintenance process carried out by the maintenance unit in accordance with the outputs from the timer(s) when either of the following conditions are satisfied:
Condition 1: The non-print period of time is greater than the third period of time and the elapsed time is greater than the second period of time but less than the first period of time; or
Condition 2: The elapsed time exceeds the first period of time. Under this condition, the non-print period of time is not used.
Thus, in the ink jet recording apparatus of the present invention arranged as described above, consideration is given to executing the head maintenance process from the end of the second period of time until the first period of time at which time the execution of the head maintenance processing is required. Between the second and first periods of time, the head maintenance process is executed when the non-print period of time exceeds the third period of time. In other words, in the present invention, there is provided a time frame (between the second and first periods of time) during which printing is carried out in preference to the head maintenance process. During this time frame the head maintenance process will only be performed if no printing occurs and no print command is issued for the third period of time. If no such activity occurs during that third period of time within the above-mentioned time frame, it is assumed that the apparatus is not currently being used and executes the head maintenance process. However, once the elapsed time exceeds the first period of time the head maintenance process is executed immediately after any print operation currently being performed is completed. After the execution of each head maintenance operation, the control sequence is reset to begin the measuring and comparing process again.
By providing a time frame in which to execute the head maintenance process without disrupting the printing process, the ink jet recording apparatus of the present invention eliminates or at least minimizes any interruptions to the printing process in order to accommodate the head maintenance process. The first period of time represents the time at which the head maintenance process must be performed and is generally determined by the type and model of the apparatus being used. However, the second and third periods of time may be set in accordance with the manner-in which the apparatus is used.
Control of the head maintenance process may also be based on the amount of print generated by the recording head since the last head maintenance process was performed. The amount of print generated may be quantified by the number of lines printed and may be used instead of, or in addition to, the elapsed time measurement. In either case, the ink jet recording apparatus includes a counter that counts the number of lines printed by the recording head since the recording head was last subjected to the head maintenance process and compares that count with a first print amount (i.e., a first predetermined number of lines) and a second print amount (i.e., a second predetermined number of lines) which is less than the first print amount. A timer measures a non-print period of time during which no printing is executed by the recording head and compares the non-print period of time with the third period of time. The head maintenance drive controller directs the execution of the head maintenance process which is carried out by the maintenance unit in accordance with the outputs from the counter and the timer when either of the following conditions are satisfied:
Condition 3: The non-print period of time is greater than the third period of time and the amount of print is greater than the second print amount but less than the first print amount; or
Condition 4: The amount of print exceeds the first print amount. Under this condition, the non-print period of time is not used.
Controlling the head maintenance process based on the amount of print generated since the last head maintenance process also overcomes the disadvantage in conventional systems of prolonging a series of successive print operations while the head maintenance process is executed.
The maintenance unit may comprise a pump for forcibly drawing ink from the nozzles of the recording head and discharging it to the outside. Alternatively or in addition to the pump, the maintenance unit may comprise a head wiping mechanism which may include a blade for wiping away foreign matter adhered to the nozzle forming surface of the recording head.
Methods for maintaining an ink jet recording apparatus and in particular for controlling the execution of the head maintenance process are also provided in accordance with the above-described control schemes. Such methods may be implemented by a program of instructions (i.e., software) which may be embodied on a device-readable medium.
Other objects and attainments together with a fuller understanding of the invention will become apparent and appreciated by referring to the following description and claims taken in conjunction with the accompanying drawings.